Short of bigger drums and shoes (nigh on impossible given the limited clearance to the front wheels already).....I think there is one path worth pursuing (though I haven't just yet)....I recently saw one of the Wheeler Dealer shows. Mechanic/host Edd China was refurbishing an older drum braked car (Volvo or VW, can't remember)...While retrofit discs were available, he chose instead some shoes w/ improved friction material which purportedly provided 30% more stopping power, within a fraction of the performance of disc brakes....There are quite a few specialty brake/friction outfits about.....might be worth checking into. I'll do that shortly myself.
As I replied before I just do a lot of down shifting. I can do all of the passes here in CO and never touch the brakes on the downhill parts, actually I need to hit the skinny pedal. I did manage to slide through a stop light as my Jeep was pushing me through it. I probably piss off a lot of people as my brake lights don't come on until I am doing around 5 MPH.
Mine sucked for many miles after I bought it but it got better.
As I remember... Amesz00 has fitted some aftermarket shoes to his truck that are supposed to have better breaking efficiency.
I have not seem any posts from him about this "mod", but I for one would be interested in knowing if using different shoes has made any difference.
Having said this, no matter what shoes you change to, the drums on these trucks are primarily designed to stop the truck when it is going forwards. so this change would likely make little difference in enhancing the braking capabilities when the truck is going backwards.
The only way I see to resolve that problem would be to convert to disks, but that is in no way a small change.
something very wrong .... low vacuum and pedal to the floor are potentially inconsistent, possibly two problems.
foot to the floor is either air in the hydraulic system or brake shoe adjustment too loose.
it may be that excessive movement of the pedal uses more vacuum, if after fixing the brakes there's still a problem start checking for leaks, usually round the servo but can be in perished pipes or pump not working well.
I drive like unka, I've never seen the low vacuum light on.